Nutritional improvement of sorghum grain by yeast fermentation and its effect on performance and egg quality of laying hens

Nguyen Tuyet Giang^1,2, Le Thi Thuy Hang^1,2 and Le Thi Thuy Loan^1,2

¹ An Giang University, An Giang, Vietnam
ntgiang@agu.edu.vn
² Vietnam National University Ho Chi Minh City, Vietnam

Abstract

This study consisted of two experiments. In the first experiment, sorghum grains were fermented using two products of baker yeast under two moisture levels of the substrate. The results showed that fermentation with S. cerevisiae in low-sugar dry yeast Instant Success and 50% initial moisture content of the substrate significantly improved the nutritional value of sorghum grains after 72h by increasing the CP content. This optimal fermented sorghum meal was then used in the second experiment, where 120 Isa Brown laying hens were assigned to four dietary treatments with 0% (FS0), 3% (FS3), 5% (FS5) and 7% (FS7) fermented sorghum meal. It showed that the inclusion of fermented sorghum meal improved laying rate and feed conversion ratio, with no significant effects on egg quality traits. Among the treatments, the 7% inclusion level of fermented sorghum meal was found to be the most favourable, as it improved production performance without causing negative impacts on the egg quality.

Keywords: baker yeast, Isa Brown chicken, feed conversion ratio, anaerobic fermentation, laying rate, sorghum grain

Introduction

Poultry production plays a significant role in providing high-quality protein sources to millions of consumers globally, enhancing food security and promoting sustainable agricultural practices (FAO 2013; Sheffield et al 2024). However, the rapid growth of the global poultry industry and the feed-food competition have raised concerns and demands for innovative strategies to sustain the development. Given that feed represents about 60-70% of total production costs in poultry farming, the reliance on the conventional feed ingredients such as soybean and maize has increasingly challenged by price volatility and the competition between the feed and biofuel sectors. Therefore, identifying alternative, cost-effective feed ingredients has become an urgent priority, not only to reduce the production costs but also improve the environmental sustainability of poultry farming (Alshelmani et al 2024; Bist et al 2024).

Sorghum (Sorghum bicolor) is one of the leading cereal crops worldwide and ranked the fifth highest production of the cereal crops, following maize, wheat, rice and barley, with 57.3 million tons of annual production globally (FAOSTAT 2023). Sorghum diversifies into four major categories, encompassing grains sorghum, sweet sorghum, forage sorghum and biomass sorghum (Tanwar et al 2023). They have been recognized for their adaptability and dynamic nutritional profile with high dietary carbohydrate, fiber and phytochemical substances such as polyphenols, tannins, sterols and phytic acid (Nemukondeni et al 2022). In terms of nutritive value, cost and availability, sorghum grain is probably the next alternative to maize grains in animal feed as they contain lower ME but higher in CP levels than maize. The protein content of sorghum grain is higher than that of maize but about equal to wheat. Its energy value is also rated as high as 90-100% of maize depending on the livestock species. Therefore, sorghum appears to be well suited as a substitute for maize in animal feed (Etuk et al 2012; Abdulkadir et al 2013; McDonald et al 2022). To improve the nutritional value of sorghum and expand its applicability in poultry feeding systems, new processing technologies are required.

Among relevant strategies, fermentation has proved efficient in improving the nutritional value of various feedstuffs. Using baker's yeast Saccharomyces cerevisiae, solid- or liquid- state fermentation have been known as the oldest practice of biotechnology which prolong preservation, enhances flavour and reduces antinutritional compounds in products of plant origin (Sandhu et al 2017). For cereal, biological compounds found in fermented products include protein, essential amino acids, vitamins, minerals, mannan oligosaccharide, beta-glucan and varieties of unexplained growth-promoting substances. The combination of these metabolites improves poultry health by regulating the immune system, intestinal health, nutritional digestibility and enhances poultry production performance (Bilal et al 2022; Zhang et al 2022; Fathima et al 2023). Current findings have shown that yeast fermentation greatly enhanced the nutritional value of broken rice by increasing its crude protein (CP) and reducing crude fiber (CF) contents. These improvements are beneficial to nutrient digestibility and growth performance in several animal species such as ruminant animals, chickens and pigs (Preston 2023; Tran et al 2023; Nguyen et al 2023; Nguyen et al 2024).

Many studies have documented the positive impacts of fermentation on different cereals, but there still appears to be a knowledge gap concerning the effects of yeast fermentation on the sorghum grains with respect to the commercial laying hen’s production performance and egg quality. Addressing this notable gap, this research aimed to investigate the value of fermented sorghum meal to enhance the layer production.

Materials and methods

The study consisted of two experiments: one to optimize the fermentation of sorghum grains and another to evaluate the effect of fermented sorghum meal on the production performance and egg quality of laying birds.

Sorghum fermentation

A 2×2 factorial experiment was conducted from January to March 2024 to investigate the effects of yeast products and moisture content on the fermentation of sorghum grain.

The red variety of Sorghum bicolor was purchased from a local feed company and ground to pass through a 300μm mesh. The chemical composition of the sorghum grains was as follows with 89.3% ± 1.01 dry matter (DM), 2.47% ± 0.13 ash, 10.3% ± 0.37 crude protein (CP), 3.08% ± 0.12 ether extract (EE) and 4.90% ± 0.21 crude fiber (CF). These values were consistent with those reported by Nemukondeni et al (2022). Distilled water was added to the sorghum meal to achieve relevant moisture content of 50% and 70%. Two commercial active dry yeast products containing Saccharomyces cerevisiae : low-sugar dry yeast Instant Success (Lesaffre, Vietnam) and high sugar-dry yeast Mauripan (AB Mauri, Vietnam) were used in this study as fermentation agents and were referred to as yeast A and yeast B, respectively.

The flow diagram of the fermentation process is summarized in Figure 1. Initially, yeast cells of S. cerevisiae were activated by dissolving 1 g of dry yeast powder in 100 mL of 10% glucose solution and incubated for 24h at room temperature (RT). The fermentation process was performed anaerobically in a plastic bag at room temperature by inoculating 2% (v/w) of the yeast suspension with cell density of about 10⁸ CFU/mL into the substrates.

During the fermentation process, to determine the optimal fermentation conditions, small amount of the fermented sorghum was sampled every 24 hours up to 72 hours to monitor changes in pH value (using the pH meter, Horiba PH210, Japan) and total count of yeast cells (on the MRS agar). After sampling, all batches were oven-dried (Yamato DKN812, Japan) at 55°C until completely dry. Based on the trends of pH and yeast concentration, the optimal fermentation time was determined. The fermented sorghum meal corresponding to the optimal time point was then selected and subjected to proximate composition analysis following AOAC (2005) procedures. The results were also compared with the unfermented sorghum grains to assess improvements in nutritional value. The selected fermented meal was subsequently used as a dietary ingredient in a follow-up feeding trial on laying hens, designed to assess its effects on production performance and egg quality.

Figure 1. Flow diagram of sorghum fermentation using baker’s yeast

Animal experiment

The in-vivo experiment was conducted from April to June 2024, at a farm in Tri Ton district, An Giang province, Viet Nam. A total of 120 Isa Brown hens were distributed in a completely randomized design, with four treatments and ten replicates. The experimental period lasted for 84 days, from 22 to 34 weeks of age. The birds were provided four experimental diets, corresponding to four treatments, which contained 0% (FS0), 3% (FS3), 5% (FS5) and 7% (FS7) of the fermented sorghum meal; previously selected from the fermentation experiment. All diets were formulated to meet the requirements of the commercial laying hens (NRC, 1994), The ingredients and chemical composition of the experimental diets are presented in Table 1.

An experimental unit of 3 birds each was housed in a battery cage (50 cm × 50 cm × 40 cm), with a floor slope of 10^o. All hens were allowed unlimited access to feed and water, via individual feeders and nipple drinkers. The light regimen of 16 h light/8 h darkness time was maintained throughout the experiment.

All birds were evenly distributed in the respective treatment groups at 17 weeks old for acclimatation and data collection began at 22 weeks until 34 weeks of age. Body weight (BW) of the hens was taken at 22 and 34 weeks of age. The difference in weight at the beginning and the end of the experiment was recorded as the BW change. Eggs were collected twice daily to calculate laying rate and egg production. The daily feed intake was calculated based on the amount of feed offered and feed refused. The feed conversion ratio (FCR) was calculated as the ratio of feed intake to egg weight.

Tri-weekly (22-week, 25-week, 28-week, 31-week and 34-week), 10 eggs were randomly selected in each treatment for external and internal egg quality assessments. For external egg quality, individual egg was weighed using an electronic balance. Egg width and egg height were measured using a digital Vernier caliper. Egg shape index was calculated accordingly, using the formula: egg width × 100/egg height. For internal egg quality, eggs were carefully broken out onto a flat to measure the height and diameter of egg yolk and egg albumen (egg white) with the digital Vernier caliper. Egg shell thickness was measured using a digital thickness gauge. Egg yolk index was obtained as the ratio of egg yolk height to egg yolk diameter. The Haugh unit was calculated using the formula: 100 × log ₁₀ (h - 1.7 × w ^0.37 + 7.6), where h was albumen height (mm) and w was egg weight (g). Subsequently, the egg yolk and albumen were separated and weighed to calculate their proportion. Other parameters, such as albumen: egg yolk ratio and albumen index were also calculated.

Statistical analysis

All experimental data were subjected to statistical analysis using ng the Analysis of Variance (ANOVA) with the general linear model (GLM) procedure of Minitab 16.0. Differences among treatments were considered significant at p≤0.05.

Results and discussion

Effect of yeast products and moisture level on the nutritive value of fermented sorghum grains

Figure 2A shows a continuous decline in pH, while Figure 2B reveals a rapid increase in yeast cell counts during 72 hours of fermentation. This inverse relationship indicates active microbial fermentation, indicating active microbial metabolism and organic acid production. Notably, these trends were observed in all fermentation media, regardless of the yeast product or initial moisture level, suggesting a consistent outcome of the fermentation process under the experimental conditions. This result was typical of anaerobic fermentation processes, where acidification inhibited spoilage organisms and stabilize the final product Ojokoh and Eromosele 2015; Abdul and Webb 2017; Preston 2023).

Figure 2. Changes in pH values (A) and number of yeast cells (B) during 72h of sorghum fermentation

In this current study, due to continuous decline in pH (Figure 3A) and the maximum yeast cell density (Figure 3B), the 72-hour fermentation point was selected to assess the chemical composition of fermented sorghum, although it may not represent the absolute optimal time for anaerobic fermentation.

Table 2. further demonstrates that yeast product and moisture level significantly affected the chemical composition of fermented sorghum, particularly the CP and EE contents (p<0.05). It can be seen that most of the nutrients in chemical composition of sorghum grains were reduced by fermentation, except for CP. The nutrient loss could be due to the leaching of some soluble components into the medium. This improvement in CP content may result from the increased biomass of yeast cells after fermentation.

Figure 3. confirms the findings in Table 3, highlighting a significant increase in CP after fermentation, consistent with protein enrichment mechanisms observed in yeast-fermented substrates, as reported previously in cassava root (Inthapanya et al 2020; Vuong et al 2021) and broken rice (Nguyen et al 2024).

Figure 3. Changes in the CP content of fermented sorghum meal compared to sorghum grains (Bars with different letters are significantly different at 5% level)

As can be seen in Figure 3, the 50% moisture level produced better nutrient profiles, which aligned with optimal conditions for yeast growth shown in Figure 3, likely due to better oxygen diffusion for microbial growth. In addition, 50% moisture is more practical due to lower energy demand for drying. Based on current findings, the fermentation using yeast A and 50% initial moisture content was selected for subsequent experiment in birds.

Effect of fermented sorghum meal on production performance and egg quality of laying birds

Production results of hens given diets with four levels of fermented sorghum meal are shown in Table 3. The initial body weight (BW), the final BW of the birds at 22- and 34-weeks age, respectively and the BW change were not significantly different among treatments (p>0.05). These results indicate that the inclusion of fermented sorghum meal did not affect the chicken growth. This finding was comparable to the study of Phan et al (2020), where the supplementation of fermented maize and rice bran in diets did not significantly affect growth performance or feed intake but improved nutrient digestibility and intestinal morphology of crossbred chickens.

However, there was a significant improvement (p<0.05) in the laying rate of birds receiving diets with fermented sorghum (FS3, FS5 and FS7) relative to the control group (FS0). The feed intake and FCR were also significantly different (p<0.05) among treatments, which were also better in the fermented groups (lower feed intake and lower FCR). The laying rate of Isa Brown hens in the present study was lower than that reported for Hy-Line Brown hens (87.78-88.60%) fed diets supplemented with 2.5-7.5% fermented soybean meal, as observed by Obianwuna et al (2024). These authors suggested that fermented feed and probiotics possessed similar functions by protecting intestinal epithelium and promoting the growth of beneficial gut microbiota. The enhanced digestibility and feed efficiency may explain the superior laying performance, as observed in the present study. However, our findings were in agreement with the results of Kim et al (2017) who observed improved feed efficiency in Hy-Line Brown laying hens with the use of fermented feed ingredients. The improvements observed in the production performance may be attributed to the fermentation process, which enhanced the biological activity of cereals and improves the balance between nutrients and anti-nutritional factors, thereby promoting better nutrient utilization and overall health in poultry, as highlighted by Nguyen et al (2021), Zhang et al (2022) and Tran et al (2023).

The results in Table 4. show that there were no significant differences regarding the egg weight, eggshell thickness, shell proportion, yolk proportion, or albumen proportion, as well as albumen to yolk ratio, shape index, albumen index, yolk index and even the Haugh unit (p>0.05). Therefore, fermented sorghum meal could be used in layer diets without affecting the attributes of egg quality.

These results corroborated with the findings by Kim et al (2017) which demonstrated that dietary supplementation with fermented rice bran did not influence internal egg quality traits. These consistent outcomes can be attributed to the effects of fermentation in enhancing the quality of cereals. As explained by Zhang et al (2022), fermentation improves the biological activity of cereals by degrading anti-nutritional factors and increasing the bioavailability of essential nutrients. This biochemical enhancement may contribute to the improved production traits despite the partial replacement of conventional cereal ingredients used in animal feed.

Conclusions

The inclusion of 7% fermented sorghum meal to the diet of laying hens was shown to significantly increase production performance without negative impact on egg quality parameters.

Acknowledgments

This research is funded by An Giang University (AGU), Vietnam National University HoChiMinh City (VNU-HCM) under grant number 24.02.NN. The authors would like to gratefully acknowledge all individuals who provided technical and logistical support during the study.

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